1. Field of the Invention
The present invention relates to a video coder suitable for use in recording data representing a moving image on a record medium such as a disk or the like while compressing the amount of moving image data that is recorded.
2. Description of the Related Art
The amount of video data representing a moving image becomes enormous as compared with that of audio data, and as a result, the amount of video data has to be compressed when video data is recorded on a record medium. A recently developed technique for compressing the data amount employs a coding apparatus for compressing a data amount of video data representing a moving image and then records the compressed recording video data of a moving image on a record medium.
However, most of the conventional coders are designed to code video data in a real time fashion, and in most cases, only one path is formed, which is responsible for the following problems:
1. Encoding is not started until material data is input; PA1 2. Encoding cannot be started over again; PA1 3. Fine control, such as improving the picture quality of a particular portion is impossible; and PA1 4. The required hardware becomes large in scale because the processing must be accomplished at the frame rate.
A conventional method of compressing video data representing a moving image employs a compression system at a variable rate. In this compression method, in order to keep an image quality uniform, a large amount of codes is assigned to a complicated image and a lesser amount of codes is assigned to a simple image. Therefore, according to this method, an image of a uniform image quality that could not be obtained when video data is compressed at the fixed rate can be reproduced, and an image can be reproduced for a long period of time.
On the other hand, a record medium, such as a disk or the like has a fixed total amount of data that can be recorded thereon and cannot record data whose amount is beyond the upper limit of the total amount of data to be recorded.
Accordingly, when video data representing complicated images are made continuous is compressed at the variable compression rate and recorded on the disk, it is frequently observed that such video data exceeds the total amount of data that can be recorded on the disk and cannot be recorded on the disk.
Further, when video data representing simple images are made continuous is compressed at the variable compression rate and recorded on the disk, a recording area of the disk that should be recorded upon remains utilized.